A high capacity data storage tape includes a number of tracks (such as 16, 32, 64, 128 etc.) onto which data is written and read from by read/write elements mounted on a head. The tape (also referred to as the medium) also includes one or more servo tracks on which a pattern of servo signals has been recorded. Servo elements mounted on the head read the servo pattern and feed them into a servo control loop. The servo loop, in response, controls the position of the head to maintain the servo elements substantially centered within the servo pattern, thereby ensuring that the read/write elements are accurately aligned relative to the data tracks despite lateral movement of the tape as it travels from one reel to the other.
When a tape cartridge is loaded into a drive, a coarse motor is activated and moves the entire head assembly across the tape until the servo elements detect a servo pattern. A fine actuator, to which the servo and read/write elements are mounted on flextures, is then activated. A voice coil motor (VCM), as part of the servo loop, deflects the flextures to maintain a track following position. For high speed and accuracy, the servo loop should have a high bandwidth and the VCM driver should have a high gain. However, the high gain, as well as a sticky actuator and offsets in the digital-to-analog converter (DAC) feeding the driver, may contribute to excessive movement of the head when the fine actuator is activated. As a result, the servo elements may land outside of the areas of the tape on which the servo patterns are recorded, leading to a servo failure due to the lack of servo signal detection to feed back into the servo loop.
Consequently, a need remains for a compound tape actuator which is fast, highly accurate but is able also to reduce the possibility of overshoot when a tape cartridge is loaded into a drive.